This invention relates to an implantable cardiac stimulation lead and electrode system for applying electrical energy to an abnormally functioning heart and more particularly to an implantable pulse generator housing having electrically conductive walls serving as a defibrillation discharge electrode.
Electrodes implanted in the body for electrical stimulation of muscle or body organs are well known. More specifically, electrodes implanted on or about the heart have been used to reverse certain abnormal and life-threatening arrhythmias. Electrical energy is applied to the heart via the electrodes to return the heart to normal sinus rhythm.
Common abnormal cardiac arrhythmias include bradycardia (slower than normal heartbeat rhythm), ventricular tachycardia (faster than normal heartbeat rhythm), and ventricular fibrillation (sporadic and uncoordinated beating of the heart). The latter two arrhythmias generally are fatal if left untreated.
To control the heartbeat rhythm and prevent fatalities from ventricular tachycardia and fibrillation, several devices have been designed having the ability to stimulate the heart according to a sensed cardiac signal such as a sensed ECG signal. See for example U.S. Pat. No. 4,603,705 to Speicher et al. The Speicher et al. patent discloses a multiple electrode unitary intravascular cardiac catheter having a distal electrode for sensing and pacing, an intermediate electrode for sensing, pacing and cardioverting, and a proximal electrode for sensing and cardioverting. This multiple electrode catheter maintains the ability for heart rate sensing and low threshold pacing immediately following cardioversion.
There are many types of defibrillation cardioversion electrodes in the art. U.S. Pat. No. 4,825,871 to Cansell discloses a defibrillation/cardioversion shock system in which the box housing the pulse generator circuitry servers as a support for a discharge electrode. Specifically, the metal box is enclosed by a plastics material and a metal plate is attached to the metal box and electrically connected therewith. Charges collected by the metal plate are transmitted to the metal box, which serves as a collector. The metal box itself is not used as an electrode in the Cansell system.
The need therefore exists for implantable cardiac stimulation lead system capable of performing standard pacing, such as anti-bradycardia pacing, anti-tachycardia pacing, low-energy cardioversion, and high-energy defibrillation.